This application relates to atmospheric gas burners, and in particular relates to improvements in gas burner flame stability.
Atmospheric gas burners are commonly used as surface units in household gas cooking appliances. A significant factor in the performance of gas burners is their ability to withstand airflow disturbances in the surroundings, such as room drafts, rapid movement of cabinet doors, and most commonly rapid oven door manipulation. Manipulation of the oven door is particularly troublesome because rapid openings and closings of the oven door often produce respective under-pressure and over-pressure conditions within the oven cavity. Since the flue, through which combustion products are removed from the oven, is sized to maintain the desired oven temperature and is generally inadequate to supply a sufficient airflow for re-equilibration, a large amount of air passes through or around the gas burners.
This surge of air around the gas burners is detrimental to the flame stability of the burners and may cause extinction of the flames. This flame stability problem is particularly evident in sealed gas burner arrangements, referring to the lack of an opening in the cooktop surface around the base of the burner to prevent spills from entering the area beneath the cooktop.
The inherent cause of this flame instability is the low pressure drop of the fuel/air mixture passing through the burner ports of a typical rangetop burner. Although there is ample pressure available in the fuel, the pressure energy is used to accelerate the fuel to the high injection velocity required for primary air entrainment. Relatively little of this pressure is recovered at the burner ports. A low pressure drop across the ports allows pressure disturbances propagating through the ambient to easily pass through the ports, momentarily drawing the flame towards the burner head and leading to thermal quenching and extinction.
An additional problem is that rapid adjustments of the fuel supply to a gas burner from a high burner input rate to a low burner input rate often will cause flame extinction when the momentum of the entrained air flow continues into the burner even though fuel has been cut back, resulting in a momentary drop in the fuel/air ratio, causing extinction.
Some commercially available gas burners employ dedicated expansion chambers to attempt to improve stability performance. These expansion chambers are intended to damp flow disturbances before such disturbances reach a respective stability flame. This damping is typically attempted by utilizing a large area expansion between an expansion chamber inlet and an expansion chamber exit, typically expanding by a factor of about ten. Accordingly, the velocity of a flow disturbance entering a burner throat is intended to be reduced by a factor of about ten prior to reaching a respective stability flame, thereby reducing the likelihood of flame extinction. Large area expansion and disturbance damping are not typically present in conventional main burner ports, making conventional main burner ports susceptible to flame extinction, especially at low burner input rates. Simmer stability is generally improved as the area expansion ratio is increased. If an expansion chamber inlet is sized too small, however, the gas entering an expansion chamber may be insufficient to sustain a stable flame at the expansion chamber port.
Commercially available gas burners, such as those described in U.S. Pat. No. 5,133,658 and U.S. Pat. No. 4,757,801, each issued to Le Monnier De Gouville et al., employ an expansion chamber to improve flame stability. The De Gouville gas burners have a plenum ahead of a number of main burner ports. An expansion chamber inlet is located in the plenum, adjacent the main flame ports. When a negative pressure disturbance enters the burner (suction, for example, from the opening of an oven door), the pressure drop and flow velocity through the main burner ports are momentarily reduced causing unwanted extinction of the main burner flames. The expansion chamber flame, however, is less susceptible to extinction due to the damping effect described earlier. Although such gas burners having an expansion chamber provide somewhat improved stability performance at simmer settings, disturbances continue to cause unwanted extinction. Furthermore, these expansion chambers have excessively large flames at higher burner input rates.
Commercially available gas burners, such as those described in U.S. Pat. No. 5,800,159 issued to James Maughan overcome the issue of excessively large flames using a stability chamber that is insensitive to turn-down. The stability chamber, however, is dissimilar to the flames from the other ports and gives the burner a non-symmetric flame appearance.
Accordingly, there is a need for an improved atmospheric gas burner that is better able to withstand airflow disturbances, especially during low burner input rates.
A gas burner assembly for connection to a gas source includes a burner body having a sidewall and a main gas conduit. The burner body further includes a number of primary burner ports disposed within the sidewall, each for supporting a respective main flame. Additionally, a main fuel chamber is disposed within the burner body to provide fuel to the primary burner ports. A burner cap is disposed atop said sidewall. A stability channel is disposed within an outer portion of the burner cap. The stability channel is positioned adjacent the primary burner ports to capture a supply of gas and hot products from the burner assembly to re-ignite the primary burner ports after flameout. This configuration creates a repository of fuel and combustion products during normal burner operation within the stability channel for re-igniting the primary burner ports after flameout, thereby reducing the sensitivity of the burner assembly to pressure disturbances, while allowing a symmetric appearance to be maintained.